The use of compressed air in cylinders and rollers of printing presses is known, for example, from EP 0 298 238 A2 wherein the compressed air acts to provide force amplification by way of a pneumatic diaphragm cylinder on hydraulic work cylinders effective to clamp a printing plate on the form cylinder of a sheet fed gravure rotating press. The compressed air in the case is supplied by way of a rotating union axially of the cylinder journal.
Rotating unions for such purpose are known, as shown in catalogue 777D, 1977, "Rotating Unions" of the Deublin company. The rotating unions disclosed therein comprise a rotor which is in the form of a shaft and which is flange connected at one end, for example, to the end face of the journal of a rotating member so that its rotational axis coincides with the rotational axis of the rotating member. A tubular housing is mounted on the rotor shaft, and sealing members are so disposed between the rotor shaft and the inner bore of the tubular housing such that an annular chamber is formed for each air-conveying duct. The annular chambers can receive compressed air by way of connecting bores in the tubular housing and the compressed air thus introduced into the chambers can be conveyed onwards through bores in the rotor shaft and rotor into the rotating part. An arrangement described more particularly on page 34 of the aforesaid publication comprises a rotor shaft, tubular housing, two radially spaced-apart plain bearings and spring-biased O-rings.
The overall shapes that result from multiduct rotating unions, as well as elaborate sealing arrangements employed, are disadvantages of such rotating union systems. The use of plain bearings and O-rings for mounting and sealing is particularly disadvantageous since plain bearings require a definite fit and moments of friction arise between the tubular housing and the rotor even in the absence of transmission of compressed air. This is further disadvantageous in cases in which the compressed air is transmitted predominantly when the press is either stationary or running slowly.